1. Field of the Invention
Metal melting in a metal-melting furnace, and particularly the use of an inert gas bubble-actuated molten metal pump in a metal-melting furnace in a particularly arranged combination with a charge well of the furnace having a unique interior configuration to create a vortex therein, and advantageously additional associated apparatus, to bring metal yields and melt rates to new heights. Creation of a head of molten metal in the charge well to increase the velocity at which molten metal is discharged from the charge well into the main chamber.
2. Prior Art
The state of the art regarding the introduction of metal chips into the charge well of a metal melting furnace and the conveyance of molten metal from one place to another within or out of a metal melting furnace has been fully reviewed in my prior U.S. patents, namely, U.S. Pat. Nos. 4,702,768, 4,710,126, 4,721,457, 4,872,907, 5,211,744, 5,203,910, 5,403,381, 5,468,280 and 5,407,462, the disclosures of which patents are incorporated herein by reference.
In particular, the employment of an inert gas bubble-actuated molten metal pump for moving molten metal from one place to another in a metal-melting furnace or out of a metal melting furnace has been disclosed in my prior U.S. Pat. No. 5,203,910 as well as in my U.S. Pat. Nos. 5,403,381 and 5,468,280. A heat- and flame-resistant cover for at least a substantial portion of a charge well has been disclosed in my U.S. Pat. No. 5,211,744. Various methods and charger means for introducing metal chips into the charge well of a metal-melting furnace have been disclosed in my prior U.S. patents, in particular a stripforming briquetter device and method in my prior U.S. Pat. No. 4,702,768, a compacting extruder method and means in my prior U.S. Pat. No. 4,872,907, and a mass flow gravity feed method and apparatus for charging metal chips into the charge well of a metal-melting furnace in my prior U.S. Pat. No. 5,407,462 as well as an improved version thereof as disclosed in my published PCT application PCT/US97/15138, published as WO98/08985 on Mar. 5, 1998.
Although the inventions of these prior patents have gone far in advancing the state of the art, including the conveyance of molten metal from one place to another in a metal melting furnace or out of the metal-melting furnace, an improvement in total efficiency is always a highly-desirable objective and one which is fulfilled admirably by the provision of the present invention whereby certain of the salient features of my prior inventions and patents are combined with a novel and unique type of charge well in a manner which overcomes previous shortcomings, and greatly improves the rate of melt of new chips or scraps especially lighter grades of scrap such as turnings and small chips, into the metal pool in the charge well, the unique combination of the various aspects and elements of the invention increasing greatly the efficiency of the operation by an astute combination of the pump, the unique inner-cavity charge well, the arrangement of the pump with respect to the inner cavity of the charge well, and advantageously also the heat- and flame-resistant cover and chip charger-preferably of the gravity feed type, all together contributing to elevate the efficiency and economy of the operation to new and previously unattainable heights as further discussed hereinafter. The creation of a head of molten metal in the charge well, as compared to the level of molten metal in the main chamber, is also desirable to increase overall efficiency, and an exit port from the charge well to the main chamber of restricted internal cross-sectional area can be advantageously employed to assist with this result.
Vortexes have been created in the metal-melting industry using mechanical stirring impellers, conventional centrifugal molten metal pumps, and in some cases an electromagnetic pump. Such vortex systems as available on the market enjoy a satisfactory reputation for high volume scrap melting and create minimal difficulties and problems, but fall far short of attaining optimum melt yields. The melt yields, using existing vortex systems, particularly when melting lighter grades of scrap such as turnings and fine chips, do not achieve a satisfactory level. This is to be expected when, as is the case with such existing systems, the molten metal both enters and leaves the charge well at approximately the same level, just above the bottom of the well. It is also to be expected when one considers the number of pounds of molten metal exposed to atmosphere over a given period of time when melting in a charge well without a cover and without any inert gas acting as an antioxidant medium positioned beneath such cover atop the molten metal in the well. Published melt yield levels when melting aluminum chips by one manufacturer who employs the vortex method is approximately 90%.
According to the present invention, using the unique vortex method of submergence created using the inert gas bubble-actuated molten metal pump, especially in combination with a heat- and flame-resistant cover over the charge well or over at least a substantial portion of the cavity thereof, and especially when employing a gravity-feed metal chip charger as set forth in the foregoing and hereinafter, the melt rate can be substantially increased and the metal yield can be increased to approximately 95-97%. The invention of the present application combines the novel submerged melt vortex procedure and apparatus, advantageously with cover and furnace charger, not only for submerged melting of metal chips and scraps into the molten metal pool, but also provides stirring and circulation of molten metal throughout the furnace, especially when head pressure is established or created in the charge well by providing a greater height of molten metal in the charge well than in the main chamber, which is advantageously assisted by restricting the internal cross-sectional area of the exit port from the charge well, at or near the bottom thereof, into the main chamber, e.g., so that the internal cross-sectional area of this opening or exit port is between about 1 and 20, preferably 2 and 10, times the internal cross-sectional area of the conveying conduit or conduits which bring the molten metal to the internal cavity of the charge well at or near the top thereof. The present system can be used efficiently for lighter grades of scrap such as chips and fine turnings but, with the furnace charger elevated out of position over the charge well, allows the versatility of charging all varieties of heavy grade metal scrap directly into the charge well vortex for rapid submergence thereof without the employment of a superposed metal chip or scrap furnace charger and, if desired, without the cover.
Thus, the present invention in both method and apparatus aspects, will involve the charge well having a unique interior configuration and the associated inert gas bubble-actuated molten metal pump, bringing hotter molten metal into the interior cavity of the charge well and creating the said vortex for the rapid and efficient melting of metal chips and scraps into the molten metal mass therein. The creation of the said head of molten metal in the charge well and the head pressure which it exerts assists greatly in the melting efficiency of the vortex and in the circulation of higher-temperature molten metal throughout the system.
It may also advantageously involve the employment of a heat- and flame-resistant cover over at least a portion of the surface of the molten metal contained in the interior cavity of the charge well and, with an aperture provided in the said cover, the charge well may be surmounted by a metal scrap and chip charger, preferably of the gravity feed type, for the feeding of metal scrap and chips into the interior of the cavity through the said aperture. On the other hand, with the furnace charger out of position superposed above the charge well, all varieties of aluminum or other metal scrap may be charged directly into the vortex of the inner cavity of the charge well, either through the aperture in the cover or absent the cover. When the cover is in place, the inert gas used to actuate the molten metal pump collects beneath the cover and assists greatly in preventing oxidation of the molten metal in the inner cavity of the charge well, as we have now well established in the art.